The present invention relates to coherent information transfer and object identification systems and more particularly to an optical system and method which utilizes the synthetic aperture technique well known in the microwave art.
Several attempts have been made at object identification using coherent optics. For example, U.S. Pat. Nos. 3,532,426 and 3,597,045 disclose holographic correlation systems using inscribed codes for modulating coherent light beams. Although these attempts have been successful, they require a large number of optical matched filters prior to the actual detection of correlated signals and consequently their filters cannot be quickly accessed. By way of contrast, the present invention first detects signals and then implements the simpler and more economical electrical matched filters which can be simultaneously accessed.
The present invention provides apparatus and method for applying certain teachings of the synthetic aperture art, namely the detection of chirp signals of objects moving through the beam of an aperture, in combination with real time electronic processing of chirp signals, to the rapid reading of records and labels and to object identification. There is no known optical apparatus for using a coherent source for reading records or labels in real time. For example, the article by Barker "21 Ways to Pick Data Off Moving Objects" appearing in the October 1963 issue of Control Engineering and the article by Whittaker and Sexton "Printers and Readers Handshake for Effective Bar Code Systems" appearing in the September 1974 issue of Computer Design nowhere suggest apparatus or method for using a coherent source, much less for using a coherent source in a synthetic aperture as taught by the system of the present invention. U.S. Pat. Nos. 3,532,426 and 3,597,045 while attempting object identification using a coherent source, use the two step and time consuming reconstruction procedure of the known hologram art. Thus while coded labels are well known in the optical identification art, they can be read only in real time using non-coherent sources, or, alternatively, when more resolution of coded elements is needed, they can be read only in a two step coherent but time consuming process using the teachings of the hologram art. The system of the present invention teaches that coded records and labels can be read rapidly in real time by first detecting chirp signals and processing these signals electrically in a matched filter following their detection. The prior identification art using coherent sources reconstructs the recorded image in the two step and time consuming procedure of conventional holography and therefore while having the potential, falls short of providing apparatus and method for the rapid reading of records and labels.
Coherent optical information transfer and object identification systems are needed in the transportation, mail, stock, container, carton, packaging, etc., industries for quickly identifying objects, for example as point-of-sale identifiers in the retail industry. Presently known optical identifiers operate non-coherently by scanning bar code type labels to obtain the information. As a consequence, they are limited in their resolutions by the wavelength .lambda., the inverse aperture size D, and range R to the object. By way of contrast, the present invention offers a resolving capability which is limited only by the aperture size D.